1. Field of Invention
The invention generally relates to an optical device and a light source using the same, and more particularly, to a light guide unit and a light source module using the same.
2. Description of Related Art
In a conventional side incident type light source module, a light guide plate is used to guide a light beam emitted from a light emitting device disposed on a side surface of the light guide plate towards a front surface of the light guide plate, so as to form a uniform surface light source. For the light beam entering the light guide plate through the side surface thereof, since an incident angle of the light beam transmitted to the front surface and the back surface of the light guide plate is larger than the critical angle, the light beam is continuously totally reflected by the front and back surfaces of the light guide plate, and thus the light beam is restricted within the light guide plate.
In order to guide the light beam towards the front surface of the light guide plate, conventional techniques typically dispose optical microstructures on at least one of the front and back surfaces of the light guide plate so as to disrupt the total internal reflection phenomenon of the light beam, and thereby the light beam may be emitted from the front surface of the light guide plate. However, the position, quantity, and size of the optical microstructures typically require a finely tuned design and a suitable configuration in order for the light source module to provide a uniform surface light source. The design process is generally referred to as an optical distribution design. For example, Taiwan Patent Nos. 594074, I247142, and I287667 disclose light guide plates using microstructures to achieve the effect of a uniform light source.
One of the main reasons why an optical distribution design poses additional complexities and challenges is the minuscule dimensions of the optical microstructures (e.g., on the micrometer scale). Therefore, designing with an optical modeling software results in more errors, and the optical modeling requires a long period of time. Moreover, a scattering model of the optical microstructures is non-trivial to establish, and additional modeling errors are introduced when the quantity of the optical microstructures is too numerous. In order to overcome these errors, conventional design techniques typically perform design modifications according to the experience gained from empirical trials. Typically, three to five tests are needed to obtain an uniform surface light source. Moreover, a typical optical microstructure design employs a quantity of microstructures in the thousands, hence variables in such a design are hard to handle. The afore-described design complexities easily increase work hours, and therefore increase a manufacturing cost.
Taiwan Patent Nos. M312679, M332206, M317584, M292707, M294655, Taiwan Patent Publication No. 200617559, and U.S. Pat. No. 6,648,485 disclose a side of a light guide plate having a plurality of recess structures or protruding structures. Moreover, Taiwan Patent Nos. I253524, 594248, and M315841 disclose methods of displacing a light source. Further, Taiwan Patent Nos. 588804 and M331680 disclose disposing lenses on a light incident surface of a light guide plate.